In general, a permanent magnet synchronous motor can be fabricated to be more compact than an induction motor with respect to the same output, and accordingly, has been going to be used for drive units of a variety of systems in recent years.
Incidentally, in the permanent magnet synchronous motor, a change of an armature magnetic flux that rotates a magnetic pole is not a sine wave of a rotation angle, but contains a distortion. Therefore, torque generated by the motor pulsates since such a magnetic flux change that should originally have a sine wave shape contains the distortion, and this causes an uneven rotation and the like. Moreover, unbalance of a coil of the motor, an error in a sensor system that detects a current, and the like also cause such a torque ripple.
As a reduction method of the torque ripple, there is a method as disclosed in “Patent Document 1”, in which, since the torque ripple has association with the rotation of the motor, this association is stored in a storage device, data on the torque ripple, which corresponds to the association, is read out based on the rotation angle of the motor, and one obtained by subtracting an amount of the ripple from a torque command value is set as a new torque command value. Moreover, there is a method as disclosed in “Patent Document 2”, in which a torque ripple correction signal “Tcomp=A×sin(n×θ+p)” is arithmetically operated from such a motor rotation angle “θ”, an adjustment gain “A”, and an adjustment phase “p”, the torque ripple correction signal thus obtained is added to a target torque command in a feed-forward manner in synchronization with a rotation cycle of the motor, and the torque ripple is cancelled.
[Patent Document 1] Japanese Patent Laid-Open Publication No. H11-299277
[Patent Document 2] Japanese Patent Laid-Open Publication No. H7-129251